Optical isomerism
Optical isomerism
- Two enantiomers are mirror-image isomers.
- They are identical in almost every property — with two exceptions.
- This matters greatly for medicines.
Enantiomers and optical activity
- Enantiomers have identical physical and chemical properties, except:
- they rotate plane-polarised light in opposite directions (they are optically active).
- they may have different biological effects.
- A racemic mixture is a 50:50 mix; it gives no net rotation (the two opposite rotations cancel).
Practice
Two enantiomers differ in that they:
Enantiomers are otherwise identical; they rotate plane-polarised light oppositely and can act differently in the body.
Practice
A racemic mixture (50:50 enantiomers):
The equal, opposite rotations of the two enantiomers cancel out.
Practice
A single pure enantiomer is optically active (it rotates plane-polarised light).
A pure enantiomer rotates the plane of polarised light; only a racemic mixture cancels out.
Chirality and drugs
- A molecule with a chiral centre has two enantiomers — and they can behave very differently in the body (one may cure, the other harm).
- So drug makers either separate the racemic mixture into pure enantiomers, or use a chiral catalyst to make just the one they want.
Practice
Why does chirality matter when making drugs?
One enantiomer may cure while the other harms, so makers separate them or use a chiral catalyst.
You've got it
Key idea
- enantiomers are mirror images: identical properties except they rotate plane-polarised light oppositely and may differ in biological effect
- a racemic mixture (50:50) gives no net rotation
- chirality matters for drugs — separate the enantiomers or use a chiral catalyst